Evidence-based practices (EBPs) are increasingly being implemented in large community mental health systems. Much of the research to date has focused on policy, organizational and practitioner variables that predict adoption and initial implementation of EBPs, yet understanding sustainment is crucial to facilitate a return on costly investments in EBP development. Furthermore, most studies focus on the implementation of a single EBP, limiting opportunities to examine theoretically important predictors of implementation success concerning fit between EBPs and the contexts in which they are utilized. The proposed study will examine the impact of a major policy change mandating use of EBPs and organizational context, organizational accommodation, and practitioner attitudes and adaptations as determinants of EBP sustainment in the largest public mental health system in the United States. Our primary outcomes of interest are two aspects of sustainment: practitioner-level penetration and agency and practitioner structural and intervention fidelity to EBP models. Specific aims are as follows: (1) Characterize sustainment outcomes (Penetration, Fidelity); (2) Use mixed methods to characterize inner context factors and early implementation conditions that potentially predict EBP sustainment; (3) Identify inner context (organizational and practitioner) and early implementation conditions that determine sustainment outcomes. This project will yield new understanding of whether and how multiple EBPs can be sustained in public mental health systems undergoing a policy-driven community implementation effort. We will produce generalizable models for characterizing sustainment, including feasible and flexible measurement of fidelity across multiple EBPs. The findings will inform the development of implementation interventions to promote sustained delivery of EBPs to maximize their public health impact.